1. Field of the Invention
The present invention generally pertains to skeletal muscle stimulation, and more particularly, pertains to improved lead systems for stimulating skeletal muscle powered cardiac assist systems.
2. Description of the Prior Art
The use of skeletal muscle tissue to power chronically implantable cardiac assist systems has met with some success. See, for example, U.S. Pat. No. 4,813,952, issued to Aida Khalafalle herein incorporated by reference which describes such a system. Using the patient's own muscle tissue overcomes the problems associated with the storage and transmission of energy from artificial sources. The result is a very compact system requiring no percutaneous energy transmission.
A problem present by the use of skeletal muscle power is application of stimulation signals to cause muscle contraction. The earliest skeletal muscle powered cardiac assist systems used cardiac pacing leads for skeletal muscle stimulation.
A major improvement to such leads is found in the use of steroid eluting pacing leads. U.S. Pat. No. 4,711,251 issued to Stokes, which teaches an endocardial pacing lead having steroid drug embedded in the distal tip. This embedded steroid drug treats the heart tissue immediately in contact with the pacing electrode. U.S. Pat. Nos. 4,506,680; 4,577,642; and 4,606,118 teach similar endocardial leads, all of which treat the electrode contact area with a steroid. U.S. Statutory Invention Registration No. H356 discloses an endocardial pacing lead suitable for epicardial insertion which elutes a steroid drug from the electrode.
All of these pacing leads are directed to stimulating the heart muscle, which is configured in a predetermined shape. The skeletal muscle used to power the cardiac assist system, on the other hand, is likely to be configured in a wide variety of shapes, any specific one of which cannot be known until the surgical procedure is actually performed. For that reason a flexible, specifically designed lead is far more appropriate than one especially directed to cardiac pacing applications.